In general, decoupling capacitors, such as surface mounted device (SMD) capacitors, are disposed close to power/ground pins of electronic devices on printed circuit boards (PCBs) or the substrates of integrated circuits (ICs) to reduce undesirable noises. Capacitors are electrical devices capable of storing or absorbing electrical charges in time. That is, decoupling capacitors may provide a localized source of direct-current (DC) power for electronic devices as the signals switch simultaneously at high speed.
With the increase in signal transmission speed in ICs, unexpected interference resulting from power noises, ground bounces or simultaneous switching noises (SSN) may be serious and therefore may not be neglected for designers. However, parasitic inductances induced by conductive traces may become higher for SMD decoupling capacitors as the electronic devices operate at a high frequency. Accordingly, it may be difficult for SMD decoupling capacitors to stabilize power supply level. Additionally, SMD capacitors mounted on a PCB requires certain board space and may limit the board space available for other devices. To deal with the above problems, decoupling capacitors embedded in PCBs or the substrates of ICs may sometimes be used in power delivery network.
Embedded capacitors, which may refer to capacitors embedded or buried in a PCB, IC substrate or interposer, have been proposed to replace the SMD capacitors for eliminating switching noise. However, capacitors embedded in PCBs or the substrates of ICs, may also exhibit more inductive than capacitive when they operate at a frequency greater than its resonant frequency. That is, the impedance of the embedded capacitors may increase as the operating frequency increases, resulting in degeneration of the decoupling performance for a power delivery network. As a result, how to reduce the impedance of the embedded capacitors and broaden the decoupling bandwidth are possible considerations in power integrity design.